In digital computing systems the media of choice for storing data is quite often magnetic. Magnetic tape systems are frequently used to archive data and magnetic disk systems are used for the interactive processing of data with the central processing unit and semi-conductor memory elements.
Drive electronics units for magnetic storage devices provide an interface to the host computer system for receiving data to be written to the magnetic media and for presenting data to the host that has been read from the magnetic storage media. In magnetic storage devices a transducing head must be situated in close proximity to the magnetic media in order to write data to the media and read data from the media. Significant effort has been made to pack data ever more densely on the media while at the same time improving the write and read control functions to approach error-free operation. In the effort to produce dense recording and error-free retrieval various heads have been developed including the ferrite head, the thin film head, the metal-in-gap (MIG) head, and most recently the magneto-resistive (MR) head. Regardless of the head technology the write operation involves reversing the magnetic orientation of the media from north to south or from south to north through changes in electrical current levels from positive to negative or negative to positive. When such transitions occur at a data bit location the transition may represent a one bit while no transition at the data bit location represents a zero bit.
Limiting factors in packing data onto the magnetic media are generally associated with the read-back operation where the magnetic transition results in an electrical pulse in the head which is transferred from the head to the drive electronics unit for amplification and detection. The pulse signals at the head are extremely small and therefore subject to obfuscation. Also, increased data density narrows the window in which a transition is read and successive transitions can create shifts in the position of a sensed read pulse large enough to move the pulse out of the window and into another bit location.
Some types of head technology produce unwanted secondary pulses when reading transitions. For example, the thin film head produces perturbations in sensing transitions due to the pole tip effect, such that the desired pulse formation is clouded by leading and trailing undershoot pulses. When packing data more densely on media, the undershoot pulses tend to interfere with the accurate retrieval of other data pulses in the chain of data pulses read from the media. MIG heads may also produce somewhat similar secondary pulses but the polarity of the secondary pulse is the same as the main pulse. It is, therefore, the general object of this invention to smooth out the response obtained from such a head so that the data pulse ultimately produced by the drive electronics unit approaches a more idealized configuration.